The major objective of the proposed research is to add to our understanding of the development of phonetic competence in infants and young children and its relation to the acquisition of language. More specifically, research is proposed to investigate three aspects of speech perception: (1) the development of perceptual trading relations, that is, the use of more than one sourse of acoustic information for the categorization of speech in an integrated manner; (2) the manner in which speech is represented during the early months of life, both immediately in perception and in a relatively more permanent, long-term memory; (3) the effects of development and sensory experience on the perception of speech between the ages of 2 and 4 years. In this final series of studies, the focus will be on the categorization of speech and the effects of limited, sensory deprivation in the form of conductive hearing losses from recurrent otitis media on the processes of categorization. In all three series of studies, inferences concerning the issues at hand will be made on the basis of infants and children being able to classify and/or discriminate simple speech patterns. The experimental procedure will of course vary with the developmental level of the child. One specific goal is to provide information on the speech processing capacities of young infants, especially with respect to the abillty to utilize the multiple sources of information that exist for most phonetic distinctions. This information will help us understand how the perceptual system solves the problem of the inherent variation in speech and will inform us about the biological determinants of speech processing. With respect to the representation of speech, the immediate goal is to write a description of the mental representation of speech, and how this representation changes with development. Ultimately, this research may provide information on how the infant comes to acquire phonological rules and structures and the basic elements of a lexical network. The immediate goal of the final series of experiments is to understand the effects of one form of temporary sensory deprivation on the development of speech processing abilities. Longer-term goals are to understand how alterations in the basic processes of speech perception very early in life come to have serious and perhaps permanent consequences for the acquisition of linguistic competence and for the acquisition of academic skills later in childhood. Achieving these goals may help to provide the means to ameliorate the consequences of early deficiencies in language processing.